Effects of capillary pressures on two-phase flow of immiscible carbon dioxide enhanced oil recovery in fractured media

CO₂-EOR in a geological formation not only increases oil production but also ensures geological sequestration of CO₂. The capillary pressure is an essential factor during the process of immiscible CO₂-EOR in fractured media. Two classical capillary pressure models are adopted to investigate the effects systematically based on a unified pipe-network method. The identical capillary pressures in fractures and the rock matrixes have little effect on the fluid flow and saturation distribution of CO₂. This implies that the capillary pressure can be neglected in this condition. The effect cannot be ignored when different capillary pressures are assigned for fractures and rock matrixes. The saturation of CO₂ reaches its highest value at the fracture outlet tip if the capillary pressure in a fracture is smaller than that in the rock matrix. The phenomenon of saturation concentration of CO₂ at the fracture tip is caused by the capillary pressure difference. For non-connected fractures, the saturation concentration causes CO₂ to enter the adjacent fractures more easily. Thus, the capillary pressure difference enlarges the effect of fractures on the CO₂ flow, and shorten the breakthrough time of CO₂. Hence, both the storage amount of CO₂ and the production of oil in geological media are reduced.